Taking a quick dip in one of many lakes in the temperate region of North America this summer was not the relaxing pastime some vacationers might have hoped.
That's because it's been an "uncomfortably" bad year for "swimmer's itch." For the past decade, Simon Fraser University biologists John Webster and Bruce Leighton have been studying the condition and are now developing solutions.
Swimmer's itch is caused by a trematode parasite which moves from aquatic snails to bird or mammal hosts living at lakes. At this stage, it will attack bathing humans, burrowing into the skin. "Humans are not a suitable host for these parasites, which die shortly after the attack," explains Leighton. "The resulting swimmer's itch dermatitis is an immune reaction to the foreign protein of the dead parasite."
New control strategies being developed by SFU researchers are showing promising results. Initial results show that one method involving the physical disturbance of snail habitat in areas of high infection works as well or better than the use of chemicals, and with less impact on the lake. Chemicals are not approved for use in British Columbia largely because of their impact on fish and other wildlife, Leighton notes. "The cobble substrate of the lake that makes up the snail habitat is disturbed by turning the cobbles over with a rototiller, which is mounted on a boat and can reach down about three meters," Leighton explains, noting that similar rototillers are used at many lakes to control Eurasian milfoil. "Turning the cobbles destroys the snails that are present, exposes their eggs to predators and removes the algal coating that the snails feed on."
Leighton says snail activity is influenced by water temperatures and this year's late snow melt has kept lake temperatures low, possibly delaying the spring activities of snails into this year's tourist season. "That's why it seems like more of a problem," notes Leighton. "For anyone out for a pleasure swim, it can be an extremely uncomfortable condition."
Because swimmer's itch is caused by a number of species of the parasites, known as schistosomes, Leighton says it's crucial to know what species are causing the problem and to understand their biology and behaviour. "Another factor is the hydrology and wind patterns of the lake," he adds. "Parasites can be moved long distances from their source by surface currents."
The SFU researchers have compiled a large information base on swimmer's itch and on snail-borne disease in general, and are currently sharing the information with local chamber of commerce officials around the province.
CONTACT:
Bruce Leighton, 604-291-5586
Carol Thorbes, 604-291-3035